This invention relates to ceramic capacitors and in particular, but not exclusively, to multilayer ceramic capacitors and dielectric compositions for use therein.
A multilayer ceramic capacitor basically comprises a stack comprising a plurality of dielectric members formed of a ceramic material, with electrodes positioned between the members. The electrodes may be screen-printed onto the ceramic material, in the unfired state thereof, using conductive inks, such as plantinum, palladium and/or gold inks. A stack of screen-printed dielectric members is assembled, pressed together, cut into individual components if appropriate, and fired.
With the conventionally employed dielectrics, the capacitors must be fired at temperatures of the order of 1200.degree.-1400.degree. C., which means that the then internal electrodes must be of a suitable material to withstand such temperatures and that expensive noble metals such as platinum and palladium must therefore be used. The capacitors are fired at temperatures between 1200.degree.-1400.degree. C. until sintering occurs, in order to ensure non-porosity. The internal electrodes may be of rectangular form and cover the whole part of the area of the adjacent dielectric layers. The internal electrodes in successive layers may be laterally stepped relative to one another or have elongate portions which cross one another, as described in British application No. 7,841,677 (Ser. No. 2,032,689A) (A. L. Oliver--G. Mills 1-1).
As mentioned above, the conventional materials used for the dielectric ceramic involve high firing temperatures (1200.degree. to 1400.degree. C.) and mean that expensive noble metals have to be used for the internal electrodes. However, if the firing temperature could be reduced, by a suitable choice of the dielectric, then internal electrodes with a high silver content (50-100% silver) could be used, thus reducing costs for materials and manufacture.